The Savonius vertical axis wind turbine (VAWT) is the definitive primarily drag type vertical axis wind turbine. It uses a plurality of curved vanes which are mounted for rotation about a substantially vertical axis. In most conventional Savonius rotors, only two vanes are provided, and the vanes have generally an S-shape when viewed from above or below.
Although invented in the 1920s (see U.S. Pat. Nos. 1,697,574 and 1,766,765, for example), and despite its numerous advantages (including high torque, simplicity of construction, no need for speed limiting, not significantly affected by turbulence, no need to orient it into the wind—that is OMNI-direcitonality—and ability self-start at very low wind speed), the Savonius wind turbine has never been marketed on a significant commercial scale. Most are home made (see Making a simple Savonius wind turbine by Lance Turner, www.ata.org.au;) with rigid discs on top and bottom of each set of vanes. However, there are three common types [as described in the Turner article].
The first conventional type uses a central shaft to provide the majority of the support for the vanes. This design has the advantage of allowing the rotor to be supported only from the bottom, and can minimize weight. However, it does not have optimum efficiency.
The second and third conventional types (differing form each other only in the particular curvatures of the vanes) allow spillover of the wind from one vane to another by horizontally spacing the proximate ends of the vanes. However, this conventionally requires utilizing disc shaped solid supports above and below the vanes, and mounting structures both above and below the unit. This increases cost and limits the versatility of the units.
Another type of VAWT, which has individual Savonius rotors but mounted so that it has only some features in common with a conventional Savonius, is disclosed in U.S. Pat. No. 4,830,570. This patent shows a rotor having bearings connected to support ribs at both the top and bottom of the curved blades (vanes) and a solid exterior single central shaft remote from (not adjacent) the interior blade vertical edges (proximate edges) of both blades. In this construction the Savonius wind turbine desirable feature of omni-directionality is eliminated by mounting two rotors on horizontally spaced vertical axes with a deflector plate between them, and a partition plate with tail extending perpendicular to the deflector plate to orient the assembly into the wind.
According to the present invention, a Savonius wind turbine rotor, and wind turbine utilizing the rotor, are provided which are simple, easy and inexpensive to manufacture and assemble, yet very versatile. In the preferred embodiment, spokes are provided which mount the curved vanes of the Savonius wind turbine to a central shaft in a secure, yet typically removable, and versatile manner. The spokes and vanes are particularly configured so as to not require (although they may be provided in some circumstances) tapped holes, which would significantly increase the cost of the wind turbine and complicate its manufacture. The spokes and vanes are easy to construct—for example the spokes can be cut, with any curvature and dimensions, from relatively thick sheet material using a computer controlled device, such as a laser cutter. The vanes may be made of relatively thin sheet material, and openings for receipt of fasteners punched or otherwise formed therein, without the need for tapping. The spokes are affixed to the shaft in a simple and secure manner—which may be removable—and the vanes may then be easily assembled to the spokes by low skill labor simply using conventional fasteners like nuts and bolts.
Practice of the invention can result in an inexpensive, yet efficient, strong, long-lasting, and versatile Savonius wind turbine rotor, and turbine. The invention can be utilized to turn a generator and generate electricity, to drive a propeller on a boat, to pump water, or for a wide variety of other uses. When used to generate electricity, the turbine may readily be mounted on a flat roof of a building.
According to one aspect of the present invention there is provided a Savonius vertical axis wind turbine rotor comprising: A plurality of spokes, each spoke comprising a hub having a substantially central opening, a plurality of at least partially arcuate ribs extending substantially radially outwardly from the hub with inner and outer surfaces, and a plurality of channels defined in at least one of the inner and outer surface of each rib. A plurality of vanes of sheet material generally conforming to an inner or outer surface of a rib and having openings therein operatively aligned with the channels. And, first fasteners passing through the openings into the channels and cooperating with second fasteners provided within the channels to securely hold the vanes to the ribs, so that the vanes assume an at least partially curved configuration presenting alternately a substantially concave and substantially convex curvature to wind as the rotor rotates about a substantially vertical axis.
Preferably the openings in the ribs are non-tapped, and the first fasteners comprise bolts and the second fasteners comprise nuts.
A number of different configurations may be provided for mounting the hub to one or more central shafts. In a first example, the hub central opening has keying surface manifestations adapted to cooperate with a shaft having cooperating keying surface manifestations, to securely affix the hub to the shaft. In a second example, the hub central opening has first keying surface manifestations, and the rotor further comprises a clamp adapted to cooperate with a shaft to be securely affixed to the shaft [the clamp has second keying surface manifestations cooperating with the first keying surface manifestations so that the clamp securely affixes the hub to the shaft when clamped to the shaft]. In a third, and preferred, example, each hub itself defines a clamp adapted to cooperate with a shaft so that the hub is securely affixed to the shaft. In this case preferably the clamp comprises: surfaces of the hub defining a substantially radial slot in the hub communicating with the central opening; first and second fastener receiving elements on opposite sides of the slot and fixed to the hub; and a fastener extending between the fastener receiving elements to draw the surfaces of the hub together
Channels may be formed in the ribs, or in the hub, at opposite sides of the slot in the third example. Preferably, two or three vanes are provided, and the vanes generally conform to the outer surfaces of the ribs, and the vanes overlap the central opening so that there is spillover from one vane to the next when the rotor is rotated by wind. The desirability of spillover, for efficiency, etc., is discussed in co-pending application Ser. No. 10/854,280 filed May 27, 2004 (the disclosure of which is hereby incorporated by reference herein).
While the vanes may comprise any material suitable for practical use in a Savonius wind turbine (including highly engineered fabrics, like modern sail cloth), preferably the vanes comprise, or are characteristically similar to, aluminum sheets having a thickness of between about 10-125 thousandths of an inch, or polycarbonate having a thickness of between about 20-200 thousandths of an inch. Although the spokes may also be made of any material suitable for practical use in a wind turbine, preferably the spokes comprise, or are characteristically similar to, aluminum plates having a thickness of between about ¼-½ inch. The spokes may have cutouts formed along the length thereof for reducing weight without significantly reducing strength. Also, the vanes may have end terminations comprising bent portions abutting cooperating surfaces of the ribs, and the channels may be laser or water-jet cut into the ribs at the inner or outer surfaces thereof (in fact the entire spokes, with integral hub and ribs, may be laser or water-jet cut from standard plate).
The rotor according to the invention may further comprise at least one shaft extending through the hub substantially central openings and affixed to the hubs. The rotor is desirably in combination with a device (e. g. bearing) which mounts the shaft for rotation about a substantially vertical axis, and an output device operatively connected to the shaft, so as to define a Savonius VAWT.
A broad description of the aspect of the invention described above, yet relating to another aspect of the invention, relates to a Savonius vertical axis wind turbine rotor comprising: at least three spokes, each spoke comprising a hub having a substantially central opening, two or three at least partially arcuate ribs substantially integral with the hub and extending substantially radially outwardly from the hub; a plurality of vanes of sheet material generally conforming to the ribs; and a plurality of removable fasteners operatively connecting the spokes to the vanes so that the vanes assume an at least partially curved configuration presenting alternately a substantially concave and substantially convex curvature to wind as the rotor rotates about a substantially vertical axis.
The interconnection between the spokes and vanes and shaft may be as set forth above. As an alternative connection of the spokes and vanes, channels are defined in a bottom or top surface of each of the ribs, with a plurality of cross-bores in the ribs intersecting the channels; each vane has top and bottom edges co-operable with the rib channels to substantially securely fit therein; and a plurality of openings are positioned to align with the cross bores in the channels; and the fasteners pass through the bores and channels to securely hold the vanes to the ribs.
Picking up on the last description, that is according to another aspect of the invention a Savonius vertical axis wind turbine rotor is provided comprising: A plurality of spokes each spoke comprising a hub having a substantially central opening, a plurality of at least partially arcuate ribs extending substantially radially outwardly from the hub with channels defined in a bottom or top surface of each of the ribs, and a plurality of cross-bores in the ribs intersecting the channels. A plurality of vanes of sheet material each generally conforming to the ribs, each vane having: top and bottom edges cooperable with the rib channels to substantially securely fit therein; and a plurality of openings positioned to align with the cross bores in the channels. And, a plurality of fasteners passing through the bores and channels to securely hold the vanes to the ribs so that the vanes assume an at least partially curved configuration presenting alternately a substantially concave and substantially convex curvature to wind as the rotor rotates about a substantially vertical axis.
The fasteners may each comprise a bolt passing through a bore from an outer or inner surface of the rib and connected to a nut adjacent the inner or outer surface of a rib. Also, the vanes may comprise, or be characteristically similar to, aluminum sheets having a thickness of between about 10-125 thousandths of an inch, and the ribs comprise, or may be characteristically similar to, aluminum plates or bars.
According to another aspect of the present invention there is provided a Savonius VAWT spoke comprising: A hub having a substantially central opening therein for receipt of a shaft. A clamp associated with the hub adjacent the substantially central opening (e. g. for deforming the central opening so as to clamp the spoke on a shaft). A pair of ribs substantially integral with the hub and extending substantially radially outwardly from the hub; the ribs having at least partially curved inner and outer surfaces. And, a plurality of surface manifestations formed in at least one of the inner and outer surfaces of the ribs for receipt of fasteners to hold vanes to the ribs. The ribs have distal tips, and preferably the surface manifestations are substantially T-shaped openings in at least the outer surfaces of the ribs, and overlap the central opening on opposite sides of the hub. The spoke may further comprise wind flow directors mounted on the ribs extending substantially from the distal tips to the hubs. The spoke is preferably formed by laser, plasma, or water jet cutting from a sheet of material, e. g. of or having characteristics similar to aluminum plate having a thickness of between about ¼-½ inch. Preferably the aluminum is anodized.
It is the primary object of the present invention to provide an improved Savonius VAWT, and rotor and spoke components thereof, which can be easily, securely, and cost-effectively constructed for use for almost any purpose to which a VAWT can be put. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.